As an ion beam device, a focused ion beam device and an ion milling device are known. These devices are used in sample manufacture when carrying out slice observation of fault locations of a wafer using a TEM (Transmission Electron Microscope), or SEM (Scanning Electron Microscope) for example. In particular, since an FIB device scans a sample surface with a sufficiently focused ion beam and can perform accurate slice processing of specific sites such as defects while detecting secondary electrons generated at the time of scanning and observing as an image, FIB devices are widely used as evaluation devices for semiconductor manufacturing processes.
The schematic structure of a conventional FIB device is shown in FIG. 6. The main parts of this FIB device are an ion source 100, an ion optical system 101, a secondary charged particle detector 102, a gas gun 103, a sample holder 104 and a sample stage 105.
The ion source 100 is a liquid metal ion source exemplified by Gallium (Ga), for example. The ion optical system 101 is for focusing an ion beam from the ion source 100, as well as scanning the ion beam on the sample 106, and has a condenser lens (electrostatic lens), beam blanker, movable aperture, 8-pole stigmeter, objective lens (electrostatic lens) and scanning electrodes etc. arranged in order from the side of the ion source 100. The secondary charged particle detector 102 is for detecting secondary charged particles generated when a sample 106 is scanned by a focused ion beam (hereinafter simply referred to as FIB) 100a. It is then possible to obtain an observed image (SIM image) using a Scanning Ion Microscope (SIM) by carrying out image processing based on these detection results.
The sample stage 105 can be controlled along five axes. With five axes of control, it is possible to control three dimensional movement in the XYZ directions, rotation around an axis (Z-axis) perpendicular to the XY plane, and tilt. The sample holder 104 is for fixing the sample 106, and the sample is conveyed on the sample stage 105 mounted on a moving platform called a boat (not shown in the drawings). The sample 106 is, for example, a wafer. A gas gun 103 is for blowing a prescribed gas for forming a deposition film as a protective layer on the surface of the sample 106.
Next, a description will be given of the basic sample manufacturing sequence that uses the above described FIB device. A series of procedures for manufacturing a TEN sample using a method referred to as a “pick up” method (or lift out method) are shown schematically in FIG. 7(a) and FIG. 7(b). In the following, the manufacturing sequence for a TEM sample will be described with reference to FIG. 6 and FIG. 7.
First, a wafer constituted by a sample 106 is fixed on the sample stage 105. Coarse positioning is then carried out in such a manner that an FIB 100a from an ion source 100 is irradiated in the vicinity of this defect location based on position information for the defect location provided in advance. Next, the vicinity of the defect location is scanned by the FIB 100a, and the position of the defect location is specified (position outputted) while looking at an SIM image obtained by this scan. After detecting the position, prescribed gas is blown onto the surface of the wafer by the gas gun 103, and a deposition film (protective film) is formed by scanning a prescribed range including the defect location of the surface of the wafer using the FIB 100a. Forming of this deposition film is typically referred to as ion assist deposition (or ion beam CVD (Chemical Vapor Deposition)) and a deposition film can be selectively formed at a portion irradiated by the FIB 100a. 
Continuing on, as shown in FIG. 7(a), the vicinity of the defect portion of the wafer surface is irradiated by the FIB 100a so as to be coarsely processed, and the processed portion is irradiated with the FIB 100a so as to be subjected to finishing processing. In this processing, the FIB 100a is irradiated from a normal direction with respect to the surface of the wafer, the surface of a region irradiated by the FIB is gradually removed, and finally the cross section 107a shown in FIG. 7(b) is obtained. The extent to which the thickness of the cross-section 107a as viewed from above can be made thin changes depending on the material of the sample and the acceleration voltage of the TEM used. For example, it is necessary to make this thickness 0.1 μm or less in the case of observing a lattice image of an Si group semiconductor sample using a TEM of an acceleration voltage of 200 k. Further, in the event that 3D analysis etc. is carried out by tomography using a TEM, thickness of the sample can by finished to the order of 0.5 μm.
Finally, after the angle of incidence to the wafer of the FIB100a is adjusted by controlling the tilt angle of the sample stage 105, by processing using the FIB100a, a notch 107b (portion shown by the broken line in FIG. 7(b)) as shown in FIG. 7(b) is formed at the periphery of the portion where the cross-section 107a is formed. A portion taken out along the notch 107b containing the cross section 107a is constituted by the TEM sample 107.
A dedicated device (manipulator) is used to take out the TEM sample 107. FIGS. 8(a) and (b) show an example of taking out the TEM sample using the pick-up method.
First, the tip of a probe 108 made of glass approaches the cross section 107a of one side of the TEM sample 107 made by the procedure of FIG. 7. When the tip of the probe 108 comes close to the cross section 107a to a certain extent, as shown in FIG. 8(a), the TEM sample 107 becomes stuck by electrostatic to the tip of the probe 108. The probe 108 is then moved to above an organic film 109 having viscosity prepared separately with the TEM sample 107 remaining in a state of being fixed to the tip, and as shown in FIG. 8(b), the TEM sample 107 stuck to the tip is placed on the organic film 109. The TEM sample 107 is fixed by the viscosity of the organic thin film 109 and is taken away from the tip of the probe 108.
The organic thin film 109 to which the TEM sample 107 is fixed is then carried to another TEM device separate from the FIB device, and observation of the cross section 107a of the TEM sample 107 is carried out. Recently, composite FIB devices incorporating observation devices such as scanning electron microscopes and energy distributed X-ray detectors etc. and manipulators etc. in an FIB device have also been proposed, with observation from sample manufacture being carried out using a single FIB device.
In addition to the methods of manufacturing a TEM sample using a pick-up method described above, methods also exist for making TEM samples by making a small sample for a specific location by splitting up a wafer using a dicing saw, fixing this small sample to a dedicated sample holder and carrying out crosssectional processing.
However, in either of the methods for manufacturing described above, the processing surface (cross section) is subjected to damage by the FIB during cross-sectional processing by the FIB. FIG. 9(a) is a cross-sectional view of a portion of the TEM sample 107 of FIG. 7(b), and FIG. 9(b) is a partial enlarged view thereof. In FIG. 9, the deposition film 110 is a protective film formed at the time of cross section processing by the FIB.
In cross sectional processing using an FIB, damage is incurred by the surface of the cross section 107a of the TEM sample 107 and part of the ions contained in the FIB are injected so that a damaged layer (fragmented layer) 111 is formed as shown in FIG. 9(b). The damage layer 111 has an amorphous state with a mixture of elements originally included in the sample itself and injected ions (Ga). If the unwanted damage layer 111 is formed on the surface to be observed (cross section 107a) in this way, the damage layer proves a hindrance and it is not possible to carry out TEM observation, and in particular, clear lattice image observations, in a satisfactory manner. This kind of damage layer problem also similarly occurs in SEM sample manufacture.
A method of removing the damage layer by etching (ion milling) using a low energy ion beam, for example, an argon (Ar) ion beam has been proposed. For example, in Japanese Patent publication No. 3117836 (Japanese Patent Laid-open No. Hei. 6-260129), there is disclosed an FIB device capable of removing a damage layer, having a built-in ion milling device.
FIG. 10 is a schematic view showing an outline of the structure of an FIB device disclosed in the above publication. The main elements of this FIB device are a liquid metal ion beam irradiation device 200, a gas ion beam irradiation device 201, and a sample stage 202.
The liquid metal ion beam irradiation device 200, is equipped with an ion optical system as shown in FIG. 6, and is capable of scanning specified parts of the surface of the sample 203 mounted on the sample stage 202 using a sufficiently focused ion beam (FIB) drawn out from a liquid metal ion source. The liquid metal ion source is, for example a Ga ion source.
The gas ion beam irradiation device 201 uniformly irradiates a region of a prescribed range including a section that has been sliced with a gas ion beam drawn out from a gas ion source. The gaseous ion source may be, for example, an Ar ion source. A gaseous ion beam is not necessary for convergence as with an FIB. It is therefore not possible to provide an ion optical system that sufficiently converges an ion beam such as that provided in a liquid metal ion beam irradiation device 200 in a gaseous ion beam irradiation device 201. An ion optical system for sufficiently converging an ion beam is extremely expensive and a low cost is achieved by not using this.
With the above described FIB device, first of all, the sample 203 is subjected to slice processing with an FIB from the liquid metal ion beam irradiation device 200. The damaged layer is formed with the cross section shown in FIG. 9(b) during cross section processing. After slice processing, a region containing the slices section is irradiated, and the damage layer on the slice is similarly removed by etching.
There is also damage to the slice caused by the gas ion beam irradiation, but only to a small extent. The thickness of a damaged layer in the case of a gaseous ion beam is of the order of a number of nm whereas the thickness of a damaged layer is 20 to 30 nm in the case of a liquid metal ion beam. This damaged layer is therefore not a problem in observation of cross sections using a TEM or SEM.
As described above, in the case of slicing processing using a FIB, since it is possible to have a damage layer on the processed slice, there is a problem in that it is not possible to carry out favorable slice observation for a TEM or SEM etc.
By removing the damage layer after slice processing with the FIB using the gas ion beam, the above described problem is solved, but in this case, a new problem arises with regard to re-attachment of secondary particles due to irradiation with a gaseous ion beam, as will be described in the following.
The process where the secondary particles become reattached is shown schematically in FIG. 11(a) to FIG. 11(c). As shown in FIG. 11(a), an Ar ion beam is irradiated in order to remove the damage layer 111 formed on the slice. The irradiation range of the Ar ion beam includes an adjacent surface 204 adjoining the slice. If the Ar ion beam is irradiated to the adjacent surface 204, then secondary particles 205 are ejected from the adjacent surface 204, as shown in FIG. 11(b). Secondary particles 205 ejected from this adjacent surface 204 are attached to the slice after the damage layer 111 has been removed, forming the re-attachment layer 206 as shown in FIG. 11(c). The components of the reattachment layer 206 are ambiguous and hinder effective cross section observation.
The object of the present invention is to solve the above described problems, and to provide an ion beam device and ion beam processing method capable of preventing re-attachment of secondary particles to a surface of observation (cross section).